The temperature controller for a clothes dryer consists of a bimetallic switch mounted on an electrical heater attached to a wall-mounted insulation pad.
The switch is set to on at 70°C, the maximum dryer air temperature. To operate the dryer at a lower air temperature, sufficient power is supplied to the heater such that the switch reaches 70°C
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Fundamentals of Heat and Mass Transfer
- 2.2 A small dam, which is idealized by a large slab 1.2 m thick, is to be completely poured in a short Period of time. The hydration of the concrete results in the equivalent of a distributed source of constant strength of 100 W/m3. If both dam surfaces are at 16°C, determine the maximum temperature to which the concrete will be subjected, assuming steady-state conditions. The thermal conductivity of the wet concrete can be taken as 0.84 W/m K.arrow_forward8.15 A mercury bath at is to be heated by immersing cylindrical electric heating rods, each 20 cm tall and 2 cm in diameter. Calculate the maximum electric power rating of a typical rod if its maximum surface temperature is .arrow_forward1.67 In beauty salons and in homes, a ubiquitous device is the hairdryer. The front end of a typical hairdryer is idealized as a thin-walled cylindrical duct with a 6-cm diameter with a fan at the inlet that blows air over an electric heating coil as schematically shown in the figure. The design of this appliance requires two power settings, with which the air blown over the electric heating coil is heated from the ambient temperature of to an outlet temperature of and with exit air velocities of 1.0 m/s and 1.5 m/s. Estimate the electric power required for the heating coil to meet these conditions, assuming that heat loss from the outside of the dryer duct is neglected.arrow_forward
- A manufacturer of ice cream freezers claims that its product has a coefficient of performance of 1.3 while freezing ice cream at 250 K when the surrounding environment is at 300 K. Is this claim valid?arrow_forwardA thermocouple shielded by aluminum foil of emissivity 0.15 is used to measure the temperature of hot gases flowing in a duct whose walls are maintained at Tw. = 380 K. The thermometer shows a temperature reading of Tth = 530 K. Assuming the emissivity of the thermocouple junction to be 0.7 and the convection heat transfer coefficient to be h = 120 W/m 2 C . determine the actual temperature of the gas. What would the thermometer reading be if no radiation shield was used?arrow_forwardA classroom that normally contains 40 people is tobe air-conditioned with window air-conditioning units of 5-kW cooling capacity. A person at rest may be assumed todissipate heat at a rate of about 360 kJ/h. There are 10 lightbulbs in the room, each with a rating of 100 W. The rate ofheat transfer to the classroom through the walls and the windows is estimated to be 15,000 kJ/h. If the room air is to bemaintained at a constant temperature of 21°C, determine the number of window air-conditioning units requiredarrow_forward
- The fast and efficient cooking of microwave ovens made them one of the essential appliances in modern kitchen. Discuss the heat transfer mechanisms associated with the cooking of a kitchen in microwave and conventional ovens , and explain why cooking in microwave oven is more efficient.arrow_forwardThe cylinders that come out of the heat treatment furnace are cooled in a stagnant air environment in a horizontal position. The cylinders have a diameter of 100 mm and a length of 0.1 m. The temperature of the cylinders is 440 ° C and the ambient temperature is 20 ° C. Calculate the heat transfer from 10 cylinders to the environment. a) 3125 W b) 2350 W C) 1848 W d) 1354 W e) 2750 Warrow_forwardShow an external data to support the claim that the consumers living within regions with hot climate will buy the stainless steel pan with digital thermometer reading that is powered by the heat generated while cooking and that sales will be higher in summer.arrow_forward
- Discuss briefly the different types of heat loads which have to be taken into account in order to estimate the total heat load of a large restaurant for summer air conditioning?arrow_forwardThe 8-mm-thick bottom of a 220-mm-diameter pan may be made from aluminum (k = 240 W/m · K) or copper (k = 390 W/m · K). When used to boil water, the surface of the bottom exposed to the water is nominally at 110°C. If heat is transferred from the stove to the pan at a rate of 600 W, what is the temperature of the surface in contact with the stove for each of the two materials?arrow_forwardIn a food industry, pieces of meat with approximately 30 cm in diameter and 20 mm in thickness are stored in a industrial freezer and thawed by exposure to ambient air at 15°C with convective heat transfer coefficient equal to 10W/(m2.K). Consider a piece of meat that, when removed from the freezer, had a temperature of -12°C. For defrosting, the piece is hung on a "line", so that both larger surfaces are exposed to the ambient air. For frozen meat, the following properties can be assumed ρ=1090 kg/m3, cp=3.54 kJ/(kg.K), k=0.47 W/(m.K). Ask: (1) Indicating the control volume and the simplifications adopted, obtain the differential energy balance equation for the cooling the piece of meat and describe the conditions of outline and initial that apply to the process, justifying them; (2) Use the appropriate analytical solution to determine the time necessary for the complete defrosting of the part. The part is considered to be completely thawed when a minimum temperature of 5oC is reached…arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning